l8o TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



possess such durability or strength. In this country it is fairly 

 common in small plantations. It is possible that the yield of 

 seed from these might be seriously affected by the insect. A 

 comparison of the area of distribution of the Douglas fir and of 

 Abies fwbilis shows that a very considerable part of the areas is 

 common to both. It would be natural to conclude that the 

 home of the Douglas is also the home of its seed parasite, and 

 both have adapted themselves well to conditions in this country. 

 The seed parasite of the Douglas is now a well-known enemy : 

 a similar adaptation of host and parasite may result in the case 

 of Abies nobilis unless a suitable remedy can be found and 

 applied. 



I desire to thank the Rev. James Waterston (Imperial Bureau 

 of Entomology) for so kindly informing me of the previous 

 records, and also Dr Stewart MacDougall, for directing me in 

 my search for the identity of the specimen. 



29. Note on Beneficial Insects. 



By R. Stewart MacDougall, M.A., D.Sc. 



In the war against injurious insects natural aids are present in 

 mammals, birds, insects and fungi. The so-called Beneficial 

 Insects are sometimes distinguished into those which are 

 predaceous, moving about in search of insects which they 

 devour, and those which are parasitic, feeding externally on the 

 host insect or living inside the host insect, and, by feeding at its 

 expense, destroying it. 



Predaceous insects are represented by different Ground Beetles 

 (Carabidae) and their larvae ; by Rove Beetles ; by beetles like Clerus. 

 and Rhizophagus and their allies ; by ladybirds and their larvae ; 

 by the larvae of Hover-flies ; by adult Robber Flies ; by the larvae 

 of the lacewings ; and by some Heteroptera. Some of the 

 above insects have been imported from one country to another 

 as a means of fighting some injurious species, and sometimes 

 with distinct success. One of the most successful of such 

 importations was the introduction of an Australian ladybird 

 {Vedalia cardinalis) to California. The orange groves of 

 California were being ravaged by the Fluted Scale, an accidental 

 importation from Australia. When the orange growers seemed 

 likely to be ruined a number of Vedalia cardinalis beetles were 



